JP5444793B2 - Stratified operation control device and stratified operation control method for variable compression ratio engine - Google Patents

Description

  The present invention relates to an apparatus and a method for controlling stratification operation of a variable compression ratio engine having a variable compression ratio mechanism that adjusts a mechanical compression ratio by changing a top dead center position of a piston.

  In an engine that directly injects fuel into an engine cylinder, the stratified state of the air-fuel mixture can be adjusted according to the operating state of the engine. For example, in Patent Document 1, the stratified state of the air-fuel mixture is adjusted by changing the timing of fuel injection in the compression stroke.

JP 2003-193841 A

  However, if the fuel injection timing is changed as in the conventional method described above, for example, if the fuel is injected early, the spray may come off from the cavity on the piston crown surface. . Then, it was found by the present inventors that it is difficult to form a homogeneous stratified gas mixture with a clear interface.

  The present invention has been made paying attention to such conventional problems, and a stratified operation control device and a stratified operation control method for a variable compression ratio engine capable of forming a homogeneous stratified mixture with a clear interface. The purpose is to provide.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

The present invention is an apparatus for controlling the stratification operation of a variable compression ratio engine including a variable compression ratio mechanism that adjusts the mechanical compression ratio by changing the top dead center position of the piston (33), and according to the engine operating state. The compression ratio adjustment unit (steps S16, S22, S310) increases the mechanical compression ratio as the set target stratification state is the stronger stratification state, and the engine cylinder (31a) increases as the mechanical compression ratio is increased by the compression ratio adjustment unit. ) the face is by advancing the fuel injection timing during the compression stroke from the fuel injection valve (41) provided, the compression stroke injection control unit for generating a stratified mixture of the target stratified state (step S18, S25, S313) and an ignition timing control unit (steps S19, S26, S314) for igniting the air-fuel mixture in the engine cylinder.

  According to the present invention, the mechanical compression ratio is increased as the target stratification state set according to the engine operating state is the stronger stratification state, and at the timing when the height of the piston crown surface reaches the predetermined position during the compression stroke. The fuel was directly injected from the fuel injection valve. In this way, as the mechanical compression ratio increases, the spray penetration in the compression stroke is reduced, and the interface is clear, making it easy to form a compact and high-concentration strongly stratified mixture.

It is a figure which shows an example of the variable compression ratio engine which can apply the stratified operation control by this invention. It is a figure explaining the compression ratio change method by a multiple link type variable compression ratio engine. It is a figure explaining a piston position when compression ratios differ. It is a figure explaining the in-cylinder gas density change and spray penetration change when compression ratios differ. It is the figure which illustrated the diffusion state of the fuel sprayed at the optimal timing according to the compression ratio. It is a figure which shows an example of the control map of the 1st application form of stratified operation control by this invention. It is a flowchart which shows the 2nd application form using the stratified operation control by this invention. It is a time chart when a 2nd application form is performed. It is a figure which shows the relationship between the compression ratio and the in-cylinder flow in the 3rd application form using the stratified operation control by this invention. It is a flowchart which shows the 3rd application form using the stratified operation control by this invention. It is a time chart when a 3rd application form is performed. It is a flowchart which shows the 4th application form using the stratified operation control by this invention. It is a time chart when the 4th application form is performed. It is a figure which shows other embodiment.

Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.
(Basic concept)
FIG. 1 is a diagram showing an example of a variable compression ratio engine to which stratified operation control according to the present invention can be applied.

  The inventors of the present invention have been diligently involved in a variable compression ratio engine (hereinafter referred to as a “multi-link variable compression ratio engine”) using a multi-link mechanism in which a piston and a crankshaft are connected by two links as shown in FIG. Research is repeated. In a normal engine (hereinafter referred to as “normal engine”), a piston and a crankshaft are connected by a single link (connecting rod), the mechanical compression ratio is unchanged, and the position of the piston at the top dead center is constant. However, in the multi-link variable compression ratio engine studied by the present inventors, the position of the piston at the top dead center can be changed. The present inventors have found that the stratified state of the air-fuel mixture can be controlled by using such characteristics.

  First, an example of a variable compression ratio engine to which the stratified operation control according to the present invention can be applied will be described with reference to FIG.

  The multi-link variable compression ratio engine 10 connects the crankshaft 32 and the piston 33 with two links (the lower link 11 and the upper link 12), and controls the movement of the lower link 11 with the control link 13 to perform mechanical compression. Change the ratio.

  The lower link 11 is attached to the crankpin 32b of the crankshaft 32 through a substantially central connecting hole. The lower link 11 rotates around the crank pin 32b as a central axis. The lower link 11 is configured to be split into two left and right members. The crankshaft 32 includes a plurality of journals 32a and a crankpin 32b. The journal 32 a is rotatably supported by the cylinder block 31 and the ladder frame 34. The crank pin 32b is eccentric by a predetermined amount from the journal 32a, and the lower link 11 is rotatably connected thereto. One end of the lower link 11 is connected to the upper link 12 via the connecting pin 21, and the other end is connected to the control link 13 via the connecting pin 22.

  The upper link 12 has a lower end connected to one end of the lower link 11 via a connecting pin 21 and an upper end connected to a piston 33 via a piston pin 23. The piston 33 receives the combustion pressure and reciprocates in the cylinder 31 a of the cylinder block 31.

  The control link 13 has a connecting pin 22 inserted at the tip thereof and is connected to the lower link 11 so as to be rotatable. The control link 13 is connected to the control shaft 25 through the connecting pin 24 at the other end. The control link 13 swings around the connecting pin 24. The connecting pin 24 is eccentric with respect to the control shaft 25. A gear is formed on the control shaft 25, and the gear meshes with a pinion 53 provided on the rotation shaft 52 of the actuator 51. The control shaft 25 is rotated by the actuator 51, and the connecting pin 24 moves.

  The controller 70 controls the actuator 51 to rotate the control shaft 25 to change the compression ratio. The controller 70 controls fuel injection of the fuel injection valve 41. In the multi-link variable compression ratio engine 10 of the present embodiment, the fuel injection valve 41 is arranged on the side of the combustion chamber. The controller 70 controls the ignition timing of the spark plug 42 provided in the cylinder head. The controller 70 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface). The controller 70 may be composed of a plurality of microcomputers.

  The exhaust purification catalyst 100 is disposed downstream of the exhaust passage. The exhaust purification catalyst 100 can purify the exhaust gas discharged from the engine 10 when the warm-up is completed and the catalyst component is activated.

  FIG. 2 is a diagram for explaining a compression ratio changing method by a multi-link variable compression ratio engine.

  The multi-link variable compression ratio engine can adjust the compression ratio by changing the position of the connecting pin 24 by rotating the control shaft 25 and changing the position of the piston at the top dead center.

  That is, when the connecting pin 24 is set to the position A as shown in FIG. 2C, the top dead center position (TDC) is increased as shown in FIG. 2A, and the compression ratio is increased.

  Further, as shown in FIG. 2C, when the connecting pin 24 is set to the position B, the control link 13 is pushed upward and the position of the connecting pin 22 is raised. As a result, the lower link 11 rotates counterclockwise about the crank pin 32b, the connecting pin 21 is lowered, and the position of the piston 33 at the piston top dead center (TDC) is lowered as shown in FIG. The compression ratio is lowered.

  FIG. 3 is a diagram illustrating the piston position when the compression ratio is different. 3A-1 to 3A-4 show the case of the low compression ratio, and FIGS. 3B-0 to 3B-5 show the case of the high compression ratio.

  As can be seen by comparing FIG. 3 (A-3) and FIG. 3 (B-3), in the multi-link variable compression ratio engine of this embodiment, if the compression ratio is different, the position of the piston at the top dead center is different. change. The top dead center position of the low compression ratio shown in FIG. 3 (A-3) is lower than the top dead center position of the high compression ratio shown in FIG. 3 (B-3). Since the top dead center positions are different, the low compression ratio is lower than the high compression ratio even when the piston positions at the same crank angle timing are compared. For example, comparing piston positions at a crank angle of 30 deg BTDC, the low compression ratio shown in FIG. 3 (A-1) is lower than the high compression ratio shown in FIG. 3 (B-1). In other words, the piston position at a crank angle of 30 degBTDC at a low compression ratio (FIG. 3 (A-1)) and the piston position at a crank angle of 40 degBTDC at a high compression ratio (FIG. 3 (B-0)). , Will be almost the same. The piston position at the top dead center when the compression ratio is low (FIG. 3 (A-3)), and the piston position at a crank angle of 28 degBTDC when the compression ratio is high (FIG. 3 (B-1) and FIG. B-2)) is almost the same.

  The piston position and the in-cylinder gas density are closely related. The higher the piston position, the higher the in-cylinder gas density. FIG. 4A shows the relationship between the in-cylinder gas density and the crank angle. That is, in the multi-link variable compression ratio engine of this embodiment, as shown in FIG. 4 (A), the crank angle period required until the in-cylinder gas density increases from D1 to D2 has a high compression ratio. Is the crank angle period ΔThigh, and when the compression ratio is low, the crank angle period ΔTlow. The crank angle period ΔTlow is longer than the crank angle period ΔThigh. That is, the higher the compression ratio, the faster the in-cylinder gas density changes than when the compression ratio is low. When the compression ratio is high, the in-cylinder gas density further increases and reaches D3.

  Here, when the fuel is injected at the timing T1 when the in-cylinder gas density D1 is reached when the compression ratio is high, and when the fuel is injected at the timing T2 when the in-cylinder gas density D1 is reached when the compression ratio is low, the spray penetration ( Compare penetration). Then, although the low compression ratio is injected at a later timing T2, the spray penetration is larger in the vicinity of the compression top dead center than when the high compression ratio is injected at an earlier timing T1. I understand. That is, the spray travels a longer distance.

  As can be seen from FIG. 4 (A), the present inventors know that the low compression ratio has a lower gas density in the cylinder, so that the spray resistance is small and the spray penetration is large.

  Therefore, the inventors of the present invention have devised to control the stratified state of the air-fuel mixture using such characteristics.

  That is, in the conventional normal engine, the stratified state of the air-fuel mixture in the cylinder is changed by advancing or delaying the fuel injection timing.

  However, in such a method, the distance from the injection port of the fuel injection valve to the cavity of the piston crown surface at the timing when the fuel is injected changes. In the first place, the shape of the cavity is designed so that the injected fuel can be received and the stratified state can be maintained when the piston is at the optimal position. However, if injection is performed at a different timing as in the prior art, the distance from the injection port of the fuel injection valve to the cavity of the piston crown surface at the injection timing changes, and fuel spills from the cavity. As a result, it is difficult to form a homogeneous stratified gas mixture with a clear interface.

  By the way, in the multi-link variable compression ratio engine 10 of the present embodiment, as described above, even if the piston position (distance from the injection port of the fuel injection valve to the cavity of the piston crown surface) is the same, spray penetration is performed. Can be changed. If the spray penetration is small, a compact and high-density, that is, strongly stratified mixture can be generated. The fuel injected toward the piston at the optimum design position is received by the cavity and the stratified state is maintained, and the interface becomes clear. Therefore, for example, the amount of fuel is small when performing a stratified operation.

  FIG. 5 is a diagram illustrating the diffusion state of the fuel sprayed at the optimum timing according to the compression ratio. 5A-1 to 5A-4 show the case of the low compression ratio, and FIGS. 5B-0 to 5B-5 show the case of the high compression ratio.

  As shown in FIG. 5 (A-1), when fuel is injected at an optimal timing with a low mechanical compression ratio, the subsequent increase in the in-cylinder gas density is small, so that the air-fuel mixture received in the cavity Is easy to diffuse (FIGS. 5A-2 and 5A-3). The air-fuel mixture is weakly stratified at the ignition timing (FIG. 5A-4).

  As shown in FIG. 5 (B-0), when the fuel is injected at the optimal timing with a high mechanical compression ratio, the subsequent increase in the in-cylinder gas density causes a large increase in the air-fuel mixture received in the cavity. Is difficult to diffuse (FIG. 5 (B-1) to FIG. 5 (B-4)). The air-fuel mixture is in a strongly stratified state with a compact and high concentration at the ignition timing (FIG. 5 (B-5)).

  As a method of changing the density history in the cylinder, a method of changing the effective compression ratio by changing the closing timing of the intake valve is also conceivable. However, with such a method, since the amount of air in the cylinder also changes greatly due to the change in the effective compression ratio, it is difficult to obtain the effect as in the present application.

  The inventors of the present invention have devised to control the state of the stratified mixture as described above. By applying this technology, the following devices were also created. The details will be described below.

(First application form)
FIG. 6 is a diagram showing an example of a control map of the first applied form of stratified operation control according to the present invention.

  In this embodiment, according to the map shown in FIG. 6, the mechanical compression ratio is increased as the operating state of the engine is lower in rotation and lower in load.

  In this way, if the fuel is injected at the timing when the piston reaches a predetermined position during the compression stroke with a higher compression ratio as the rotation speed is lower and the load is lower, the stratification degree of the air-fuel mixture increases, and the strong stratification with a compact and clear interface A mixture is formed. With such a stratified mixture, the contact area (wetting area) between the flame and the wall surface is reduced, so that the cooling loss is reduced and the thermal efficiency is improved.

  When the required injection amount increases as the load increases, the compression ratio is gradually reduced to form a weakly stratified mixture. In this way, the deterioration of smoke is suppressed, and the stratification region is expanded to improve the thermal efficiency. An EGR gas may be introduced into the working gas.

(Second application form)
FIG. 7 is a flowchart showing a second application form using the stratified operation control according to the present invention.

  If a strongly stratified air-fuel mixture with a clear interface can be generated as described above, the combustion stability is improved. If the combustion stability is improved, the combustion stability limit is expanded. If the combustion stability limit is expanded, the retard limit of the ignition timing is expanded. If the ignition timing can be retarded, the exhaust gas temperature can be increased, and for example, the warm-up time of the exhaust purification catalyst can be reduced.

  If the temperature of the cylinder wall surface is sufficiently high, the fuel evaporates without adhering to the cylinder wall surface even if a high-concentration stratified mixture is supplied. However, if a high-concentration stratified mixture is supplied when the temperature of the cylinder wall surface is low, the fuel may adhere to the cylinder wall surface. Furthermore, if the temperature of the cylinder wall surface is very low, such as when starting a cold machine, even if the concentration is low, the stratified gas mixture may be supplied to cause fuel wall adhesion. Therefore, when the cylinder wall surface temperature is very low, it is desirable to supply the fuel only in the intake stroke to keep the air-fuel mixture homogeneous. It is desirable to increase the stratified mixture as the temperature of the cylinder wall increases. The present embodiment has been made based on such knowledge of the inventors. Hereinafter, specific control contents will be described with reference to the flowchart shown in FIG. This flowchart is repeatedly executed every minute time when the cold machine is started.

  In step S11, the controller 70 detects the temperature of the cylinder wall surface. Specifically, for example, the temperature of the cylinder wall surface may be detected directly using a temperature sensor, or the temperature of the cylinder wall surface is estimated based on the coolant temperature at the time of engine start, the elapsed time since the engine start ( (Indirect detection).

  In step S12, the controller 70 determines whether or not the temperature of the cylinder wall surface is lower than the operation switching temperature. If it is low, the controller 70 proceeds to step S12. If it is higher, the controller 70 proceeds to step S16.

  In step S13, the controller 70 maintains the mechanical compression ratio.

  In step S14, the controller 70 retards the fuel injection timing of the intake stroke according to the temperature rise of the cylinder wall surface.

  In step S15, the controller 70 retards the ignition timing in accordance with the temperature rise of the cylinder wall surface.

  In step S16, the controller 70 increases the mechanical compression ratio in accordance with the temperature rise of the cylinder wall surface.

  In step S17, the controller 70 retards the fuel injection ratio by retarding the fuel injection timing of the intake stroke in accordance with the temperature rise of the cylinder wall surface.

  In step S18, the controller 70 increases the fuel injection ratio by advancing the fuel injection timing of the compression stroke in accordance with the temperature rise of the cylinder wall surface. As described above, as the mechanical compression ratio increases, the position of the piston at the top dead center increases. Therefore, by advancing the fuel injection timing of the compression stroke and injecting the fuel earlier, the piston position (distance from the fuel injection valve injection port to the piston crown cavity) at the fuel injection timing is kept constant. It can be maintained.

  In step S19, the controller 70 retards the ignition timing in accordance with the temperature rise of the cylinder wall surface.

  FIG. 8 is a time chart when the second application mode is executed.

  Until time t11 when the cylinder wall surface temperature reaches the operation switching temperature, the controller repeatedly performs steps S11 → S12 → S13 → S14 → S15. As a result, the mechanical compression ratio is kept constant (FIG. 8A). The fuel is injected only in the intake stroke (FIG. 8B), and the fuel injection amount is increased by retarding the injection timing in accordance with the temperature rise of the cylinder wall surface (FIG. 8C). The ignition timing is retarded according to the temperature rise of the cylinder wall surface (FIG. 8E). In this way, the exhaust gas temperature rises, so the catalyst temperature also rises (FIG. 8 (G)).

  When the cylinder wall surface temperature exceeds the operation switching temperature at time t11, the controller repeatedly performs steps S11 → S12 → S16 → S17 → S18 → S19. As a result, the mechanical compression ratio increases as the temperature of the cylinder wall surface increases (FIG. 8A). In addition to the intake stroke, fuel is also injected during the compression stroke (FIG. 8B). In the fuel injection in the intake stroke, the injection timing is retarded in accordance with the temperature rise of the cylinder wall surface (FIG. 8C), and the fuel injection ratio is reduced (FIG. 8B). In the fuel injection in the compression stroke, the injection timing is advanced according to the temperature rise of the cylinder wall surface (FIG. 8D), and the fuel injection ratio is increased (FIG. 8B). By advancing the fuel injection timing of the compression stroke and injecting fuel earlier, the piston position (distance from the fuel injection valve injection port to the piston crown cavity) at the fuel injection timing is kept constant. Can be maintained. The ignition timing is retarded according to the temperature rise of the cylinder wall surface (FIG. 8E). By doing so, the exhaust gas temperature rises, so the catalyst temperature also rises (FIG. 8 (G)).

  According to this embodiment, when the cylinder wall surface temperature is very low, fuel is supplied only in the intake stroke to make the air-fuel mixture homogeneous. Since it did in this way, fuel does not adhere directly to the cylinder, and the compression ratio is lowered, so that the influence of clevis volume is also relatively reduced and unburned components (hydrocarbon HC) Can be reduced.

  When the cylinder wall temperature exceeds the operation switching temperature, fuel is injected in the compression stroke in addition to the intake stroke. By performing fuel injection in the intake stroke in addition to fuel injection in the compression stroke, the multistage injection is performed in this way, so that the fuel is not excessively concentrated and over-rich compared to the case of single-stage injection. Can be avoided. It is possible to form a weak stratification field using the entire cylinder.

  And if it becomes a strong stratification immediately, there exists a possibility that a fuel may adhere to a cylinder wall surface. Therefore, under low wall temperature conditions, the compression ratio is lowered to form a weakly stratified mixture, and the liquid film is reduced by avoiding excessive concentration of fuel. The fuel component (hydrocarbon HC) was reduced.

  As the wall temperature rises, the compression ratio is increased to reduce the size of the stratified mixture, and by increasing the injection amount to increase the concentration of the mixture, a compact and highly concentrated stratified mixture can be formed. It becomes. By forming a highly stratified mixture in this way, a slightly rich mixture was formed around the spark plug. In this state, since the wall temperature is high, the liquid film is not a problem. As a result, the ignition stability is improved, the retard limit is increased, the exhaust temperature is increased, and the catalyst activity is accelerated, thereby reducing both unburned component (hydrocarbon HC) emission and early catalyst temperature increase. .

(Third application form)
FIG. 9 is a diagram showing the relationship between the compression ratio and the in-cylinder flow in the third application mode using the stratified operation control according to the present invention.

  As shown in FIG. 4A, the in-cylinder gas density is higher at the high compression ratio than at the low compression ratio. Therefore, as shown in FIG. 4 (B), the spray penetration becomes smaller at the higher compression ratio. As described above, the present inventors know that the high compression ratio has a higher spray resistance. Furthermore, the present inventors have also found that the higher the compression ratio, the higher the in-cylinder gas density, the greater the resistance to in-cylinder turbulence, and the more easily in-cylinder turbulence is attenuated.

  FIG. 9 shows the result of this experiment.

  Unless an intake flow control valve such as a swirl control valve or tumble control valve is used, the turbulent intensity generated in the cylinder during the intake stroke after intake top dead center is the high compression ratio indicated by the broken line. Even in the low compression ratio indicated by the one-dot chain line, it is almost the same. In the compression stroke, the high compression ratio attenuates more than the low compression ratio. This is because the in-cylinder gas density is higher at the high compression ratio than at the low compression ratio, so the resistance to the in-cylinder turbulence increases and the in-cylinder turbulence easily attenuates. .

  If an intake flow control valve such as a swirl control valve or a tumble control valve is used, the intensity of turbulence generated in the cylinder during the intake stroke after intake top dead center is large, as shown by the solid line. However, in the compression stroke, the in-cylinder turbulence is attenuated to the same extent as when the intake flow control valve is not used. It is the inventors' knowledge that this is because, if the compression ratio is high, the in-cylinder gas density is high, so that the resistance to in-cylinder turbulence increases and the in-cylinder turbulence easily attenuates.

  When a compact stratified mixture is formed at a high compression ratio, the injection timing is advanced, so that the time until ignition is longer than that at the low compression ratio. However, at a high compression ratio, the turbulence near the compression top dead center is attenuated, so that it is difficult to diffuse and it is easy to form a stratified mixture. Using these characteristics, if the first fuel is injected at any timing IT1 in the hatching area during the intake stroke using the intake flow control valve at a high compression ratio, the diffusibility of the fuel increases and becomes homogeneous. The degree can be improved. Even if the fuel is injected for the second time at any timing IT2 in the shaded region during the compression stroke, the turbulent flow is attenuated during the second injection, so that the stratified mixture will rebound such as diffusing. It does not occur.

  FIG. 10 is a flowchart showing a third application form using the stratified operation control according to the present invention. This flowchart is executed at the time of cold start.

  In step S21, the controller 70 detects the temperature of the cylinder wall surface.

  In step S22, the controller 70 increases the mechanical compression ratio according to the temperature rise of the cylinder wall surface.

  In step S23, the controller 70 enhances the intake air flow in accordance with the temperature rise of the cylinder wall surface.

  In step S24, the controller 70 retards the fuel injection timing of the intake stroke in accordance with the temperature rise of the cylinder wall surface.

  In step S25, the controller 70 advances the fuel injection timing of the compression stroke in accordance with the temperature rise of the cylinder wall surface.

  In step S26, the controller 70 retards the ignition timing in accordance with the temperature rise of the cylinder wall surface.

  FIG. 11 is a time chart when the third application mode is executed.

  The controller repeatedly performs steps S21 → S22 → S23 → S24 → S25 → S26. As a result, the mechanical compression ratio increases as the temperature of the cylinder wall surface rises (FIG. 11A). Further, the intake air flow is strengthened according to the temperature rise of the cylinder wall surface (FIG. 11 (F)). The fuel injection timing in the intake stroke is retarded according to the temperature rise of the cylinder wall surface (FIG. 11C). The fuel injection timing of the compression stroke is advanced according to the temperature rise of the cylinder wall surface (FIG. 11 (D)). The ignition timing is retarded according to the temperature rise of the cylinder wall surface (FIG. 11 (E)). By doing so, the exhaust gas temperature rises, so the catalyst temperature also rises (FIG. 11 (H)).

  In the present embodiment, fuel is injected in the compression stroke and the intake stroke. The fuel injection amount in the compression stroke and the fuel injection amount in the intake stroke were set to be approximately equal. Then, as the compression ratio increases, the injection timing in the compression stroke is advanced to reduce the size of the stratified mixture and increase the concentration. And the ignition timing was retarded. The air-fuel ratio in the entire cylinder was set to a light lean range from the vicinity of the theoretical air-fuel ratio to about A / F17. Therefore, the surplus oxygen can activate the catalyst at an early stage, and can promote the afterburning of unburned components (hydrocarbon HC).

  The injection ratio between the intake stroke and the compression stroke is approximately 1: 1. When the concentration and size of the stratified mixture are changed by the pulse width of the fuel injection amount, the controllability of the stratification degree is limited by the minimum pulse width of the injection valve, but in this embodiment, the pulse width is substantially constant. In this state, the stratification degree is controlled by the mechanical compression ratio. Therefore, the stratification degree of the air-fuel mixture can be easily adjusted regardless of the limitation on the minimum pulse width.

  Under conditions where the wall temperature is low, the compression ratio is lowered to form a weakly stratified mixture, and the liquid film is reduced by avoiding excessive concentration of fuel. The component (hydrocarbon HC) was reduced. As the wall temperature rises, the compression ratio is increased to form a highly stratified mixture, so that a slightly rich mixture is formed around the spark plug. In this state, since the wall temperature is high, the liquid film is not a problem. As a result, the ignition stability is improved, the retard limit is increased, the exhaust temperature is increased, and the activity of the catalyst is accelerated, thereby making it possible to achieve both the reduction of unburned component (hydrocarbon HC) emission and the early temperature increase of the catalyst.

  Furthermore, the intake flow is strengthened as the compression ratio increases. Mixing and diffusing of fuel injected in the intake stroke is promoted by the flow of the intake stroke, so that an air-fuel mixture with higher homogeneity can be formed in the cylinder. In the compression stroke, spray is injected into a relatively gentle flow field where the turbulence is attenuated and dissipated, so that a stratified mixture is formed near the spark plug by the momentum of the spray without being affected by the flow field. Transported. While increasing the homogeneity of the entire cylinder, it is possible to concentrate a relatively rich air-fuel mixture around the spark plug, improving the ignition stability and improving the subsequent flame propagation speed. As a result, the ignition timing retard can be increased, and the exhaust temperature rise can be further accelerated.

(4th application form)
FIG. 12 is a flowchart showing a fourth application form using the stratified operation control according to the present invention.

  In step S301, the controller 70 detects actual torque.

  In step S302, the controller 70 determines whether or not the operation mode is a transient mode. If in the transient mode, the controller 70 proceeds to step S309. If it is not the transient mode, the controller 70 proceeds to step S303.

  In step S303, the controller 70 determines whether or not the target torque has increased. Until the target torque increases, the controller 70 proceeds to step S304. If the target torque increases, the controller 70 proceeds to step S308.

  In step S304, the controller 70 maintains the mechanical compression ratio.

  In step S305, the controller 70 maintains the air-fuel ratio.

  In step S306, the controller 70 maintains fuel injection in the intake stroke.

  In step S307, the controller 70 maintains the ignition timing.

  In step S308, the controller 70 sets the transient mode as the operation mode.

  In step S309, the controller 70 determines whether or not the actual torque matches the target torque. Until they match, the controller 70 proceeds to step S310. If they match, the controller 70 proceeds to step S315.

  In step S310, the controller 70 sets the mechanical compression ratio according to the amount of deviation of the actual torque from the target torque.

  In step S311, the controller 70 sets the air-fuel ratio according to the amount of deviation of the actual torque from the target torque.

  In step S312, the controller 70 increases the fuel injection ratio in the intake stroke as the deviation amount of the actual torque from the target torque decreases.

  In step S313, the controller 70 decreases the fuel injection ratio in the compression stroke as the deviation amount of the actual torque from the target torque decreases.

  In step S314, the controller 70 retards the ignition timing as the deviation amount of the actual torque from the target torque becomes smaller.

  In step S315, the controller 70 sets the steady mode as the operation mode.

  FIG. 13 is a time chart when the fourth application mode is executed.

  Until time t21 when the target torque increases, the controller repeatedly performs steps S301 → S302 → S303 → S304 → S305 → S306 → S307. As a result, the mechanical compression ratio (FIG. 13B), air-fuel ratio (FIG. 13C), ignition timing (FIG. 13D), and fuel injection in the intake stroke (FIG. 13E) are kept constant. Is done.

  When the target torque increases at time t21, the controller processes steps S301 → S302 → S303 → S308 to set the transient mode as the operation mode.

  After the next cycle, until the actual torque matches the target torque, the controller repeatedly performs steps S301 → S302 → S309 → S310 → S311 → S312 → S313 → S314. As a result, the mechanical compression ratio is set in accordance with the amount of deviation of the actual torque from the target torque (FIG. 13B). The air-fuel ratio is set according to the deviation amount of the actual torque with respect to the target torque (FIG. 13C). At this time, the output air-fuel ratio is slightly rich. As the deviation amount of the actual torque with respect to the target torque becomes smaller, the fuel injection ratio in the intake stroke is increased and the fuel injection ratio in the compression stroke is decreased (FIG. 13E). The ignition timing is retarded as the deviation amount of the actual torque with respect to the target torque decreases (FIG. 13D).

  The driving scene of this embodiment is a transient acceleration scene. Even under the acceleration condition, the compression ratio is reduced with respect to the required torque. However, as shown in FIG. 13, there is a possibility that abnormal combustion such as knocking or pre-ignition may occur due to a delay in response of the compression ratio. .

  Therefore, in the present embodiment, split injection is performed in the intake stroke and the compression stroke, and the ignition timing is retarded, so that the stratification degree is increased under high compression ratio conditions. At the same time, the injection rate of the compression stroke is increased to form a rich stratified mixture from the spark plug to the vicinity of the center of the combustion chamber, thereby improving the flame propagation speed. In this way, abnormal combustion can be avoided. Since the air-fuel ratio at this time is set slightly higher than the stoichiometric air-fuel ratio, the specific heat of the working gas is lowered and the temperature of the end gas is lowered, so that abnormal combustion of knocking and pre-ignition can be avoided.

  Without being limited to the embodiments described above, various modifications and changes are possible within the scope of the technical idea, and it is obvious that these are also included in the technical scope of the present invention.

  For example, in the above-described embodiment, the case where the fuel injection valve 41 is disposed on the side of the combustion chamber and the cavity of the piston is used to generate the stratified mixture has been described as an example. However, as shown in FIG. 14, the same effect can be obtained even if the fuel injection valve is arranged immediately above the combustion chamber to generate the stratified mixture without actively using the cavity.

DESCRIPTION OF SYMBOLS 10 Double link type variable compression ratio engine 11 Lower link 12 Upper link 13 Control link 25 Control shaft 32 Crankshaft 33 Piston Step S16, S22, S310 Compression ratio adjustment part / compression ratio adjustment process Step S17, S24, S312 Intake stroke injection control Part / intake stroke injection control step S18, S25, S313 Compression stroke injection control unit / compression stroke injection control step Steps S19, S26, S314 Ignition timing control unit / Ignition timing control step

Claims (10)

An apparatus for controlling the stratification operation of a variable compression ratio engine having a variable compression ratio mechanism that adjusts a mechanical compression ratio by changing a top dead center position of a piston,
A compression ratio adjustment unit that increases the mechanical compression ratio as the target stratification state set according to the engine operating state is a strong stratification state;
As the mechanical compression ratio is increased by the compression ratio adjusting unit, the fuel injection timing during the compression stroke from the fuel injection valve provided facing the engine cylinder is advanced to generate the stratified mixture in the target stratified state A compression stroke injection control unit,
An ignition timing controller for igniting the air-fuel mixture in the engine cylinder;
A stratified operation control apparatus for a variable compression ratio engine, comprising: The compression stroke injection control unit generates the stratified mixture in the target stratified state by injecting fuel from the fuel injection valve at a timing when the height of the piston crown surface reaches a predetermined position during the compression stroke. ,
The stratified operation control apparatus for a variable compression ratio engine according to claim 1. The compression ratio adjustment unit increases the mechanical compression ratio as the engine operating state is a low rotation and low load.
The stratified operation control apparatus for a variable compression ratio engine according to claim 1 or 2, characterized in that An intake stroke injection control unit that generates a homogeneous mixture by injecting fuel from the fuel injection valve during the intake stroke;
When the engine is operating to warm up the catalyst,
The compression ratio adjustment unit increases the mechanical compression ratio in accordance with an increase in the wall temperature of the engine cylinder,
The intake stroke injection control unit retards the fuel injection timing in accordance with an increase in the wall temperature of the engine cylinder and decreases the fuel injection ratio.
The compression stroke injection control unit advances the fuel injection timing in accordance with an increase in the wall temperature of the engine cylinder and increases the fuel injection ratio.
The ignition timing control unit retards the ignition timing in response to an increase in the wall temperature of the engine cylinder.
The stratified operation control apparatus for a variable compression ratio engine according to claim 1 or 2, characterized in that When the engine operating state is an operating state in which the catalyst is warmed up and the wall surface temperature of the engine cylinder is lower than the operation switching temperature,
The compression ratio adjustment unit maintains the mechanical compression ratio regardless of the rise in the wall temperature of the engine cylinder,
The intake stroke injection control unit retards the fuel injection timing in accordance with the rise in the wall temperature of the engine cylinder,
The compression stroke injection control unit stops fuel injection,
The ignition timing control unit retards the ignition timing in response to an increase in the wall temperature of the engine cylinder.
The stratified operation control apparatus for a variable compression ratio engine according to claim 4. An intake stroke injection control unit that generates a homogeneous mixture by injecting fuel from the fuel injection valve during the intake stroke;
An intake flow control unit for controlling the flow strength of the intake air sucked into the engine cylinder;
Further comprising
When the engine is operating to warm up the catalyst,
The compression ratio adjustment unit increases the mechanical compression ratio in accordance with an increase in the wall temperature of the engine cylinder,
The intake stroke injection control unit retards the fuel injection timing in accordance with the rise in the wall temperature of the engine cylinder,
The compression stroke injection control unit advances the fuel injection timing in accordance with an increase in the wall temperature of the engine cylinder,
The ignition timing control unit retards the ignition timing in accordance with an increase in the wall temperature of the engine cylinder,
The intake air flow control unit strengthens the intake air flow in response to an increase in the wall temperature of the engine cylinder.
The stratified operation control apparatus for a variable compression ratio engine according to claim 1 or 2, characterized in that The wall surface temperature of the engine cylinder is detected by the coolant temperature at the time of engine start and the elapsed time from the engine start.
The stratified operation control device for a variable compression ratio engine according to any one of claims 3 to 6, characterized in that: An intake stroke injection control unit that generates a homogeneous mixture by injecting fuel from the fuel injection valve during the intake stroke;
When the engine operating state is a transient operation state where the target torque increases and the actual torque is insufficient relative to the target torque,
The compression ratio adjustment unit lowers the mechanical compression ratio in accordance with an increase in actual torque,
The intake stroke injection control unit increases the fuel injection ratio in accordance with the increase of the actual torque,
The compression stroke injection control unit decreases the fuel injection rate in accordance with an increase in actual torque,
The ignition timing control unit retards the ignition timing in accordance with an increase in actual torque.
The stratified operation control apparatus for a variable compression ratio engine according to claim 1 or 2, characterized in that The variable compression ratio mechanism is
A lower link that is freely mounted on the crankpin of the crankshaft, and
An upper link coupled to the lower link and the piston;
A control link connected to the lower link and restricting the movement of the lower link;
A control shaft that includes a swing center pin that becomes the swing center of the control link, and that adjusts the top dead center position of the piston by changing the position of the swing center pin;
The stratified operation control device for a variable compression ratio engine according to any one of claims 1 to 8, characterized by comprising: A method for controlling the stratification operation of a variable compression ratio engine having a variable compression ratio mechanism that adjusts a mechanical compression ratio by changing a top dead center position of a piston,
A compression ratio adjustment step for increasing the mechanical compression ratio as the target stratification state set according to the engine operating state is a strong stratification state;
As the mechanical compression ratio is increased by the compression ratio adjusting step, the fuel injection timing during the compression stroke from the fuel injection valve provided facing the engine cylinder is advanced to generate the stratified mixture in the target stratified state. A compression stroke injection control step,
An ignition timing control step of igniting the air-fuel mixture in the engine cylinder;
A stratified operation control method for a variable compression ratio engine.